gpu-clean-conversion: name a static pre-flight for hosts without the GPU runtime

[john-rocky]

Using this skill from a CI job and from a laptop without the GPU runtime, step 2's compile-and-compare has nowhere to run, so the first delegate feedback only arrives on a device. This adds one paragraph after step 2 pointing at a static pre-flight that reads the .tflite against a measured compatibility matrix — edge-compat, my own tool, Apache-2.0 — which names the same ops and rewrite hints without a runtime; the paragraph says explicitly that it does not replace the compile-and-compare, and that unknown means not yet measured. If an external tool does not belong in the skill, closing this is fine.